2.1. Patients and setting
We conducted a diagnostic accuracy study at the Department of Emergency Medicine, Lampang Hospital, Thailand, from May 2019 to September 2019. Patients who were older than 18 years of age with indication and no contraindications for CVC were enrolled. We obtained CVC via right internal jugular catheterization. All participants signed informed consent before enrollment. We excluded: 1) patients who refused to participate, 2) pregnant women, 3) technical errors such as blood clots or hemolysis, and 4) patients with immediate complications such as pneumothorax.
The CVC surgical equipment is all the same make and model, with a 16/16-gauge double lumen, locking both lumens to prevent air from entering. Furthermore, for blood samples' accuracy in this study's gold standard group, normal saline was not pre-cast in the CVC line. However, all patients were in Trendelenburg's position to prevent air embolism 8.
We cleaned the skin with the same 2% chlorhexidine-gluconate in 70% alcohol solution without povidone-iodine in every case before the procedure. Studies have shown that povidone-iodine may distort laboratory results 9, and 2% chlorhexidine-gluconate in 70% alcohol solution may better reduce infection 10.
After successful CVC insertion, we collected 12 ml of blood samples in the control group. The samples were then placed in blood collecting tubes, sorted according to Clinical Laboratory Improvement Amendments (CLIA) guidelines 11 labeled as a gold standard group. We flushed the line with normal saline 10 ml and used an empty syringe (10 ml empty syringe) to perform three pull-push sessions. The pull-push session included slowly pulling 10 ml blood from the line for 5 seconds duration, then gently pushing the 10 ml of blood back into the line for 5 seconds duration, and then waiting for 5 seconds before beginning the next pull-push session. We used another empty syringe to collect 12 ml blood samples and labeled them as a Pull-push group. The time from both groups of blood samples was collected until the packaging was completed for less than 3 minutes to control the environment close to the same, reduce various external influences as much as possible, and perform the laboratory results simultaneously.
The study followed through in agreement with the Declaration of Helsinki (2008) of the World Medical Association. Patient management pursued the standard of the Human Research Ethics Committee, Lampang Hospital. The Ethics Committee approved the study on 5th February 2016 (EC approval No. 19/2559).
Definition12
- Percentage error (% error): the error of the laboratory tests from the Pull-push group was compared with the gold standard using the equation:
(laboratory test results from the Pull-push group — the gold standard) x 100
laboratory test results from the gold standard
- Allowable error (%): the acceptable percentage errors as defined by the CLIA [13, 14]:
Prothrombin time (PT): ±15%;
International normalized ratio (INR): ±15%;
Activated partial thromboplastin time (aPTT): ±15%;
aPTT ratio: ±15%;
Hemoglobin (Hb): ±7%;
Hematocrit (Hct): ±6%;
White blood cell (WBC): ±15%;
Platelet count: ±25%;
Blood urea nitrogen (BUN): ±9%;
Creatinine (Cr): ±15%.
Sodium (Na): ±4 mmol/L;
Potassium (K): ±0.5 mmol/L;
Chloride (Cl): ±5%;
Bicarbonate (HCO3): ±20%; and
Blood sugar (BS): ±10%.
- Accuracy (%): The percentage of allowable error for each laboratory test. Accuracy ≥ 90% is considered highly accurate.
2.2. Study size estimation
Based on the pilot study, the mean hemoglobin of the Pull-push group and gold standard group was 8.8±2.7 vs. 9.7±2.7 gm/dL. To obtain the power of 80%, an alpha error of 5%, with a two-sided test, this study required at least 72 patients to validate the various laboratory tests.
2.3. Safety protocols
- The operative doctor must be a senior emergency medicine resident under the supervision of a medical instructor
- All patients needed a pulse oximeter, electrocardiogram, and blood pressure monitoring for safety.
- If complications might occur, Patients would immediately get care. Patients and relatives would get notified and excluded from the study.
- We monitored the complications on days 1, 2, and 7 after the procedure.
2.4. Statistical analysis
Baseline characteristics were presented by number (percentage) for categorical data and by mean±SD for numerical data. The mean value of laboratory tests between the Pull-push group and the gold standard group were compared using paired t-tests, with laboratory tests having a p-value of >0.05 being interpreted as insignificant. Mean difference and percentage error were also analyzed and presented using modified Bland-Altman plots. We calculated the accuracy for each laboratory test according to the CLIA standard.